2,248 research outputs found
Reactions of [NH3+·, H2O] with carbonyl compounds: a McLafferty rearrangement within a complex?
AbstractThe reactions of the water solvated ammonia radical cation [NH3·+, H2O] with a variety of aldehydes and ketones were investigated. The reactions observed differ from those of low energy aldehydes and ketones radical cations, although electron transfer from the keto compound to ionized ammonia is thermodynamically allowed within the terbody complexes initially formed. The main process yields an ammonia solvated enol with loss of water and an alkene. This process corresponds formally to a McLafferty fragmentation within a complex. With aldehydes, another reaction can take place, namely the transfer of the hydrogen from the CHO group to ammonia, leading to the proton bound dimer of ammonia and water, and to the NH4+ cation. Comparison between the available experimental results leads to the conclusion that the McLafferty fragmentation occurs within the terbody complex initially formed, with no prior ligand exchange, the water molecule acting as a spectator partner
Designing multifunctional chemical sensors using Ni and Cu doped carbon nanotubes
We demonstrate a "bottom up" approach to the computational design of a
multifunctional chemical sensor. General techniques are employed for describing
the adsorption coverage and resistance properties of the sensor based on
density functional theory (DFT) and non-equilibrium Green's function
methodologies (NEGF), respectively. Specifically, we show how Ni and Cu doped
metallic (6,6) single-walled carbon nanotubes (SWNTs) may work as effective
multifunctional sensors for both CO and NH3.Comment: 24th International Winterschool on Electronic Properties of Novel
Material
Computational design of chemical nanosensors: Transition metal doped single-walled carbon nanotubes
We present a general approach to the computational design of nanostructured
chemical sensors. The scheme is based on identification and calculation of
microscopic descriptors (design parameters) which are used as input to a
thermodynamic model to obtain the relevant macroscopic properties. In
particular, we consider the functionalization of a (6,6) metallic armchair
single-walled carbon nanotube (SWNT) by nine different 3d transition metal (TM)
atoms occupying three types of vacancies. For six gas molecules (N_{2}, O_{2},
H_{2}O, CO, NH_{3}, H_{2}S) we calculate the binding energy and change in
conductance due to adsorption on each of the 27 TM sites. For a given type of
TM functionalization, this allows us to obtain the equilibrium coverage and
change in conductance as a function of the partial pressure of the "target"
molecule in a background of atmospheric air. Specifically, we show how Ni and
Cu doped metallic (6,6) SWNTs may work as effective multifunctional sensors for
both CO and NH_{3}. In this way, the scheme presented allows one to obtain
macroscopic device characteristics and performance data for nanoscale (in this
case SWNT) based devices.Comment: Chapter 7 in "Chemical Sensors: Simulation and Modeling", Ghenadii
Korotcenkov (ed.), 47 pages, 22 figures, 10 table
Grain Surface Models and Data for Astrochemistry
AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions
Computational Design of Chemical Nanosensors: Metal Doped Carbon Nanotubes
We use computational screening to systematically investigate the use of
transition metal doped carbon nanotubes for chemical gas sensing. For a set of
relevant target molecules (CO, NH3, H2S) and the main components of air (N2,
O2, H2O), we calculate the binding energy and change in conductance upon
adsorption on a metal atom occupying a vacancy of a (6,6) carbon nanotube.
Based on these descriptors, we identify the most promising dopant candidates
for detection of a given target molecule. From the fractional coverage of the
metal sites in thermal equilibrium with air, we estimate the change in the
nanotube resistance per doping site as a function of the target molecule
concentration assuming charge transport in the diffusive regime. Our analysis
points to Ni-doped nanotubes as candidates for CO sensors working under typical
atmospheric conditions
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